The present invention is directed generally to ink jet inks, and, more particularly, to ink jet inks having both improved waterfastness and smearfastness.
Ink jet prints formed from ink jet inks employing water-insoluble colorants, such as pigments, typically do not have very good smearfastness, even though other properties of the ink are improved with the presence of the colorant. This is due to the fact that the inks are water-based. Dispersants are designed to xe2x80x9csolubilizexe2x80x9d the colorant particles, and as a consequence, the ink is rendered more susceptible to smear, such as when using a highlighter pen.
Emulsion polymer systems have been developed to co-print with the colorants, which, upon drying, create polymeric films that protect the colorant from abrasion and chemical attack. However, these additives are, in many instances, quite difficult to formulate for ink jet applications.
The present invention is an improvement over U.S. Pat. No. 6,090,749, issued Jul. 18, 2000, to the present inventor and assigned to the same assignee as the present application. The ""749 patent is directed to a method for applying clear, vivid, and water-fast printed images to a substrate, and employs an ink containing a sublimable dye diffusion thermal transfer coloring agent. The substrate includes a backing layer and an ink absorbent layer on the backing layer. The backing layer is designed to receive the coloring agent therein after sublimation of the coloring agent. While the patent is quite useful for its intended purpose, it requires a special print medium, comprising a specialized multi-layer substrate.
There remains a need for an ink jet ink that employs water-insoluble colorant, together with a dispersant, which is both waterfast and smearfast and is suitable for printing on common print media, such as paper.
In accordance with the present invention, a method of printing an ink jet ink on a print medium is provided, wherein the resulting printed ink is both waterfast and smearfast, employing a water-insoluble colorant. The method comprises:
(a) providing an aqueous-based ink containing at least one disperse, sublimation dye and at least one dispersant for dispersing the dye;
(b) jetting said ink onto the print medium to form an intermediate printed image; and
(c) subjecting the print medium to a combination of heat and pressure for a period of time to convert the intermediate printed image to the waterfast and smearfast printed image. The temperature is high enough to cause the disperse, sublimation dye particle to disintegrate and diffuse into the media.
Further in accordance with the present invention, the aqueous-based ink as described above is employed in combination with an ink jet printing unit, including an ink jet printing cartridge containing the aqueous-based ink jet contained therein. The ink jet printing unit is configured to print images on a print medium, and the ink jet printing unit is also associated with apparatus for applying heat and pressure to images printed on the print medium.
The approach of the present invention does not require the addition of polymers to the ink; rather, it takes advantage of the change of state of the sublimation dispersed dye solid to gas to solid, shedding the solubilizing dispersant, and yielding in effect a solvent dye that is not soluble in water and unaffected by abrasion. Smear data provide evidence of the increased smearfastness afforded by the method of the present invention.